Wind-induced responses of super-large cooling towers

Traditional gust load factor(GLF)method,inertial wind load(IWL)method and tri-component method(LRC+IWL)cannot accurately analyze the wind-induced responses of super-large cooling towers,so the real combination formulas of fluctuating wind-induced responses and equivalent static wind loads(ESWLSs)were derived based on structural dynamics and random vibration theory.The consistent coupled method(CCM)was presented to compensate the coupled term between background and resonant response.Taking the super-large cooling tower(H=215 m)of nuclear power plant in Jiangxi Province,China,which is the highest and largest in China,as the example,based on modified equivalent beam-net design method,the aero-elastic model for simultaneous pressure and vibration measurement of super-large cooling tower is firstly carried out.Then,combining wind tunnel test and CCM,the effects of self-excited force on the surface pressures and wind-induced responses are discussed,and the wind-induced response characteristics of background component,resonant component,coupled term between background and resonant response,fluctuating responses,and wind vibration coefficients are discussed.It can be concluded that wind-induced response mechanism must be understood to direct the wind resistant design for super-large cooling towers.

Wind-induced vibration of single-layer reticulated shell structures

Aiming at the dynamic response of reticulated shell structures under wind load,systematic parameter analyses on wind-induced responses of Kiewitt6-6 type single-layer spherical reticulated shell structures and three-way grid single-layer cylindrical reticulated shell structures were performed with the random simulation method in time domain,including geometric parameters,structural parameters and aerodynamic parameters.Moreover,a wind-induced vibration coefficient was obtained,which can be a reference to the wind-resistance design of reticulated shell structures.The results indicate that the geometric parameters are the most important factor influencing wind-induced responses of the reticulated shell structures;the wind-induced vibration coeffi-cient is 3.0-3.2 for the spherical reticulated shell structures and that is 2.8-3.0 for the cylindrical reticula-ted shell structures,which shows that the wind-induced vibration coefficients of these two kinds of space frames are well-proportioned.

A More Precise Computation of Along Wind Dynamic Response Analysis for Tall Buildings Built in Urban Areas

Modern tall buildings are generally built in urban areas, where value of the terrain roughness length is much greater than that of the general terrain areas, therefore wind-induced vibrations become more pronounced. The present formulas of numerical analysis of wind-induced response become less accurate. A more accurate expression of along-wind load spectrum matrix is proposed. On the basis of the expression, structural analysis formula of along-wind displacement and acceleration response are developed and programmed. The rationality of these formulas are illustrated in examples.

Statistical extremes and peak factors in wind-induced vibration of tall buildings

In the structural design of tall buildings, peak factors have been widely used to predict mean extreme responses of tall buildings under wind excitations. Vanmarcke＇s peak factor is directly related to an explicit measure of structural reliability against a Gaussian response process. We review the use of this factor for time-variant reliability design by comparing it to the conven- tional Davenport＇s peak factor. Based on the asymptotic theory of statistical extremes, a new closed-form peak factor, the so-called Gamma peak factor, can be obtained for a non-Gaussian resultant response characterized by a Rayleigh distribution process. Using the Gamma peak factor, a combined peak factor method was developed for predicting the expected maximum resultant responses of a building undergoing lateral-torsional vibration. The effects of the standard deviation ratio of two sway components and the inter-component correlation on the evaluation of peak resultant response were also investigated. Utilizing wind tunnel data derived from synchronous multi-pressure measurements, we carried out a wind-induced time history response analysis of the Common- wealth Advisory Aeronautical Research Council （CAARC） standard tall building to validate the applicability of the Gamma peak factor to the prediction of the peak resultant acceleration. Results from the building example indicated that the use of the Gamma peak factor enables accurate predictions to be made of the mean extreme resultant acceleration responses for dynamic service- ability performance design of modem tall buildings.

Wind Pressure Distribution and Wind-induced Dynamic Response for Spatial Groined Latticed Vaults

The wind pressure distribution and wind-induced vibration responses of long-span spatial groined latticed vaults （SGLVs） were numerically simulated, which always are ones of the most important problems in the structural wind resistance design. Incompressible visco-fluid model was introduced, and the standard k - two equation model and semi-implicit method for pressure linked equation （SIMPLE） were used to describe the flow turbulence. Furthermore, the structural dynamic equation was set up, which is solved by Newmark-fl method. And several sort of wind-induced vibration coefficients such as the wind-induced vibration coefficient corresponding to the nodal displacement responses and wind loads were suggested. In the numerical simulation where the SGLV consisting of the cylindrical sectors with different curved surface was chosen as the example, the influence on the relative wind pressure distribution and structural wind-induced vibration responses of the closed or open SGLV caused by such parameters as the number of cylindrical sectors, structural curvature and the ratio of rise to span was investigated. Finally, some useful conclusions on the local wind pressure distribution on the structural surface and the wind-induced vibration coefficients of SGLV were developed.

Wind-induced vibration control of Hefei TV tower with fluid viscous damper

The Hefei TV tower is taken as an analytical case to examine the control method with a fluid viscous damper under wind load fluctuation.Firstly,according to the random vibration theory,the effect of fluctuating wind on the tower can be modeled as a 19-dimensional correlated random process,and the wind-induced vibration analysis of the tower subjected to dynamic wind load was further obtained.On the basis of the others'works,a bi-model dynamic model is proposed.Finally,a dynamic model is proposed to study the wind-induced vibration control analysis using viscous fluid dampers,and the optimal damping coefficient is obtained regarding the wind-induced response of the upper turret as optimization objectives.Analysis results show that the maximum peak response of the tower under dynamic wind load is far beyond the allowable range of the code.The wind-induced responses and the wind vibration input energy of the tower are decreased greatly by using a fluid viscous damper,and the peak acceleration responses of the upper turret is reduced by 43.4%.

大跨索屋盖结构风振动力计算新方法研究

大跨索屋盖结构风振动力响应复杂,传统采用等效静力风荷载计算其风致振动响应的适用性一直是当前大跨结构研究的热点。针对下凹型(单层马鞍形索网)和上凸型(轮辐式双层索网、索穹顶、弦支穹顶)四类典型大跨索屋盖结构,以四类结构风洞试验测试数据为基础,结合最近邻点插值方法研究提出了基于节点动力风荷载(模式一)和面组分区动力风荷载(模式二)两种荷载取值计算模式及其计算流程,并与传统基于等效静力风荷载的取值计算模式(模式三)进行对比,在四种不利风向角下探究四类典型索屋盖采用三种荷载取值模式时的风致振动响应。结果表明,基于模式一与模式二计算得到的索屋盖结构风振响应均较模式三要高,采用节点风荷载的取值计算模式一能更为精确地反映屋盖结构实际承担的风荷载,有效表征屋盖结构的实际风振响应;在上下游均无临近场馆影响下,下凹型和上凸型索屋盖的平均和脉动风振位移响应云图总体分布规律较为一致,但响应大小变化规律不一,下凹型呈现中间大、周边小的逐渐递减的规律,而上凸型屋盖呈现中心区域小、中间环带大、周边再次下降的变化规律。